In Fig. REF (c), we observe that \(A_1\)  increases linearly with \(H\) , which confirms a constant in-plane magnetic moment \(m=A_1/H=0.124\pm 0.005 \, \mathrm {Nm/mol/T}\)  \((0.0075\pm 0.0003 \, \mu _\mathrm {B}/\mathrm {Mn})\) , constant with that found in the irreversible torque in Fig. REF (a). As shown in Fig. REF (d), \(m\)  is temperature-independent up to \(T \approx 275\,\mathrm {K}\) , which is still far below the Néel temperature. This evidences the intrinsic correlation of the ferromagnetic and antiferromagnetic orders [1]}, [2]}, [3]}, [4]}, as discussed in Sec. .
On the other hand, from the \(A_2\)  component we can obtain the susceptibility anisotropy \(\Delta \chi \equiv \chi _{ab}-\chi _{c}\) , where \(\chi _{c}\)  and \(\chi _{ab}\)  are the out-of- and in-plane susceptibilities, respectively, because the field-induced magnetization produces a torque equal to
\(\frac{1}{2}\Delta \chi H^{2}\sin {2\theta }\)  [5]}, [6]}. In Fig. REF (c), we show that \(A_2\)  is negatively proportional to \(H^2\)  and obtain \(\Delta \chi =-0.0278 \mathrm {m^3/mol}\)  at \(T=4\,\mathrm {K}\) , which is consistent with the previous studies [2]}, [1]}. Figure REF (d) indicates that \(\Delta \chi <0\)  in the temperature range below \(275\,\mathrm {K}\)  and tends to go to zero as the temperature increases.
The low-temperature susceptibility anisotropy reflects the strength of the Dzyaloshinskii-Moriya interaction [9]}, while the high-temperature behavior \(\chi _{ab} \rightarrow \chi _{c}\)  ought to be the signal of suppression of magnetic anisotropy as the Néel temperature is approached from below.
It is worthy to note that the data in Fig. REF (d) are taken from the two distinct samples with masses of \(1.45 \, \mathrm {mg}\)  and \(0.0157\,\mathrm {mg}\) , where the \(0.0157\,\mathrm {mg}\)  is derived from the torque signal since it is far too small to measure on an ordinary balance.
